Nano-size doesn't seem to play a crucial role in this application. The article is concerned with Italcementi's TX Active cement. Italcementi's main development is a photocatalytic hydraulic binder, and here's their patent:

https://data.epo.org/publication-server/getpdf.jsp?pn=094645...

In the patent, they claim that

"Any kind of photocatalyst able to oxidize in the presence of light, air and environmental humidity (oxygen and water) the polluting substances contacting the surface of the hydraulic binder (or the relative mortars and concretes) in a hardened state is part of the present invention, particularly a titanium dioxide, mainly in the form of anatase, or a precursor thereof, optionally doped with other atoms different from Ti."